I'm flying the Dreamliner from Helsinki this winter, sadly in Economy. Though if you were flying Y I'd say the HEL option is the best since the 787 offers a better layout, as well as the flight time being much shorter from HEL than CDG.

But since you're flying Business Class I would rather have chosen CDG, since you get a longer flight time, hence being able to enjoy the service more. Also the seats on the 777 are fully flat, whereas those on the 787 are not. I suppose that should make for a rather easy decision.